1. Field of the Invention
The present invention relates to a system having a plurality of devices connected via communication lines and, more particularly, to a system in which power is supplied through the communication lines.
2. Related Background Art
There exist conventional systems for data transfer in which a plurality of devices including a hot-plug-connectable device are connected via a power line and a data bus. FIG. 22 is a block diagram to show a configuration example of a bus system according to a conventional example. The conventional bus system has such structure that a plurality of devices Axe2x80xa2101 to Exe2x80xa2105 are connected via power line 109 and data bus 108. In the figure reference numerals 110, 111 designate plugs connected to an AC 100V power supply. The conventional bus system is configured so that log information, which is history records (records of activities) of the respective devices under system connection, is stored only in the device Axe2x80xa2101 which is a host device.
The above conventional technology, however, had the following issue. Specifically, in the conventional bus system, the host was only one device storing the log information being the history records of the respective devices under system connection. This caused such a drawback that the log information disappeared when the host was disconnected during action of the system.
Meanwhile, Universal Serial Bus (USB) and IEEE1394 are drawing attention as interface buses for personal computers. These interfaces incorporate a power line, taking easiness and convenience of connection thereof into account.
However, supplied power also has to be limited with consideration to the load on the power supply of the host device and USB has the current limitation of 5 V and max 500 mA according to the standard thereof. In the USB host device, i.e., on the power supply side, when the load current of USB devices under connection exceeds the aforementioned current limit value, a protection circuit is activated to interrupt the power supply to the USB devices.
The conventional USB devices, however, had the following problem.
Among potential devices as USB devices, there are devices necessitating a large current drain in a short and transient period, though an average power consumption of such devices is low. For example, it occurs upon activation of a motor in a disk device such as a floppy disk drive, during a large sound output in a loudspeaker system incorporating an amplifier, and so on.
Although this transient power is of the short period of time, it is not practical to cover it by a capacitor or the like, because the necessary capacitance thereof is too large. In such cases, therefore, a conceivable countermeasure heretofore was either one of a method of designing the device so as to be active within the range of power supply capability at the expense of performance of the device and a method of giving a higher priority to the performance of the device. However, when the higher priority was given to the performance of the device, the power supply to the device had to be supplied from an outside power other than the USB interface bus and this posed the problem of degrading convenience and simplicity of USB.
For example, when a stereo speaker system using the USB interface is intended to design, the maximum power that can be achieved by the power supply of 5 V and 500 mA (250 mA per channel) is only 625 mW per channel even with no loss. Further, in order to gain the maximum output in an Output Transformer Less (OTL) state, the impedance of the speakers is limited to 20 xcexa9, which is not a normally practical value, unless a DC-DC converter or the like is used. The maximum power is 3.13 W under the conditions of the power-supply voltage 5V, the impedance 4 xcexa9 of the ordinary speakers, and OTL.
An example of conventional display devices is one as illustrated in FIG. 23.
FIG. 23 is a block diagram to show the structure of the conventional display device.
This display device 612 is provided with hub 512, MPU 513, display part 514, switch 611, and ROM 613.
The hub 512 transmits data from personal computer (PC) 511 to digital camera 517, scanner 518, printer 519, and MPU 513 connected to the hub 512. It also transmits data from digital camera 517, scanner 518, printer 519, and MPU 513 connected to the hub 512, to PC 511.
The digital camera 517 accepts a specification command of photography and image number, a specification command of image data or the like, or data from PC 511 via hub 512 and sends data such as image data or the like and data such as photography conditions or the like to PC 511 via hub 512. The scanner 518 accepts the resolution, position, and range of scan, and commands etc. from PC 511 via the hub 512 and sends image data to PC 511 via hub 512.
The printer 519 accepts a control command and print data from PC 511 via hub 512 to carry out printing and sends the printer status to PC 511 via hub 512.
The MPU 513 accepts various set values of the display part 514 from PC 511 via hub 512 and sends the monitor status to PC 511 via hub 512. It can also accept input of various set values from switch 611 and performs setting of the display part 514 by use of the various set values thus accepted.
The display part 514 undergoes various adjustments from MPU 513 and accepts image data from PC 511 to present a display thereof.
In the case of the conventional display device described above, however, the operation such as the display or printing of image data was not able to be carried out when the display device was in a disconnected state from the computer or when the power of the computer was off.
As described above, the log information disappears when the host device storing the log information being the histories of the respective devices under system connection is disconnected. Further, when the USB or the like is used as an interface bus, the supplied power has to be limited with consideration to the load on the power supply of the host device.
Therefore, the present invention is directed to a system that permits succession of the history information of each device even if any device is disconnected and that permits efficient utilization of power.
The present invention has been accomplished in view of the above points and an object of the present invention is to provide a system, a control method, and a memory medium that permit succession of the past history information of each device (information of activity records) even if any device is disconnected and that permit efficient utilization of power while suppressing power demand by setting a device with fewer activities in the past into a power saving mode, even if demanded power is over supply.
In order to accomplish the above object, the present invention provides a bus system to which a plurality of devices driven under supply of power can be connected, wherein each of at least two devices out of the said devices comprises memory means for storing history information of each device under connection to the system and control means for altering the history information in the memory means when an alteration occurs in a configuration of the system.
The present invention also provides a bus system to which a plurality of devices driven under supply of power can be connected, wherein each of at least two devices out of the said devices comprises memory means for storing history information of each device under connection to the system and control means for altering the history information in the memory means when an alteration occurs in a configuration of the system and for performing such control that a total demanded power of the devices does not exceed a total supplied power.
In view of the aforementioned problems in the conventional technology, another object of the present invention is to provide a power control apparatus and a power supply control method of USB equipment that can assure the convenience and simplicity of USB without degrading the performance of USB equipment, and also provide a USB apparatus equipped with this power control apparatus.
In order to accomplish the above object, a power control apparatus according to the present invention is a power control apparatus for a driving device to which power is supplied from a power supply device which is subject to current limitation at a predetermined current limit value, the power control apparatus comprising a rechargeable battery, and a charge control part for charging the battery when a current drain is lower than the limit current value, wherein current is supplied from said battery to the driving device when the current drain exceeds the limit current value.
A USB apparatus according to the present invention is a USB apparatus comprising a driving device to which power is supplied from a power supply device which is subject to current limitation at a predetermined current limit value, and a power control device connected to the power supply device via a USB connector and arranged to control power supply to the driving device, wherein the power control device comprises a rechargeable battery, and a charge control part for charging said battery when a current drain is lower than the limit current value and wherein current is supplied from the battery to the driving device when the current drain exceeds the limit current value.
In view of the aforementioned problems in the conventional technology, another object of the present invention is to provide an information processing apparatus, a display control apparatus, a display control method, and a memory medium that permit the operation such as display, printing, or the like even if a computer is disconnected or even if the power of the computer is off.
In order to accomplish the above object, an information processing apparatus according to the present invention comprises means for distributing upstream bus means serially connected to an upstream device, to downstream bus means serially connected to a plurality of downstream devices, wherein when energization from the upstream bus means is present, data from the upstream device is transmitted to the downstream bus means and wherein when the energization from the upstream bus means is absent, said means is connected to an image input/output device connected to the downstream bus means to effect transfer of image data thereto or therefrom.